Wet combustion of waste liquors

ABSTRACT

1. A TWO-STAGE CONTINUOUS METHOD OF WET COMBUSTION OF A WASTE LIQUOR OBTAINED FROM THE SODA PROCESS FOR THE PULPING OF WOOD AND CONTAINING COMBUSTIBLE COMPONENTS, WHICH METHOD COMPRISES THE SERIALLY SUCCEEDING STEPS OF MIXING A STREAM OF THE WASTE LIQUOR WITH HEATED OXYGENATING GAS UNDER PRESSURE; PASSING THE MIXTURE OF A TEMPERATURE BETWEEN 450* AND 705*F. AND UNDER A PRESSURE BETWEEN 70 TO 225 ATMOSPHERES UPWARDLY THROUGH A FIRST REACTION ZONE IN THE LOWER COMPARTMENT OF A GENERALLY VERTICAL PRESSURE VESSEL WHEREIN TO EFFECT COMBUSTION OF A MAJOR PART OF THE COMBUSTIBLES CONTENT OF THE STREAM INTO AN INERT GASEOUS PHASE COMPRISING CARBON DIOXIDE AND STEAM, WITH GENERATION OF HEAT; PASSING THE RESULTING PARTIALLY OXIDIZED MIXTURE COMPOSED OF GASEOUS PHASE AT ELEVATED TEMPERATURE, UNDER PRESSURE UPWARDLY INTO A SECOND REACTION ZONE IN AN UPPER COMPARTMENT OF SAID PRESSURE VESSEL, THE SAID PARTIALLY OXIDIZED MIXTURE BEING PASSED AS A STREAM UPWARDLY THROUGH BUT OUT OF DIRECT CONTACT WITH LIQUID PHASE IN THE SECOND REACTION ZONE AND BEING THEN DISTRIBUTED INTO SAID SECOND REACTION ZONE ABOVE SUCH LIQUID PHASE; SEPARATING THE SAID INERT GASEOUS PHASE FROM LIQUID PHASE OF THE PARTIALLY OXIDIZED MIXTURE IN THE UPPER PART OF THE SECOND REACTION ZONE, DISCHARGING THE SAID INERT GASEOUS PHASE FROM THE UPPER PART OF THE SAID SECOND REACTION ZONE, THEREBY REDUCING THE PARTIAL PRESSURE OF THE INERT GASEOUS PHASE IN EQUILIBRIUM WITH THE SAID LIQUID PHASE, CAUSING THE SEPARATED LIQUID PHASE TO FLOW DOWNWARDLY AS A COLUMN OF LIQUID IN SAID SECOND REACTION ZONE, THE TEMPERATURE OF THE DOWNWARDLY FLOWING COLUMN OF LIQUID BEING AT A TEMPERATURE BETWEEN 450* AND 705.4*F. AND UNDER A PRESSURE BETWEEN 70 AND D225 ATMOSPHERES; SUBJECTING THE RESIDUAL COMBUSTIBLES CONTENT OF SAID DOWNWARDLY FLOWING COLUMN OF LIQUID, SUBSTANTIALLY FREE FROM THE AFORESAID GASEOUS PHASE TO FURTHER OXIDATION TREATMENT BY PASING AN OXYGENATING GAS UNDER PRESSURE UPWARDLY THROUGH SAID COLUMN OF LIQUID, THEREBY FORMING A FURTHER GASEOUS PHASE AND A SUBSTANTIALLY COMBUSTIBLES-FREE LIQUID PHASE, THE PARTIALLY PRESSURE OF OXYGEN IN CONTACT WITH THE LIQUID PHASE IN THE SECOND REACTION ZONE BEING AT LEAST AS GREAT AS THE PARTIAL PRESSURE OF OXYGEN IN CONTACT WITH THE LIQUID PHASE IN THE FIRST REACTION ZONE, AND THE TEMPERATURES IN THE FIRST REACTION ZONE AND IN THE SECOND REACTION ZONE BEING SUBSTANTIALLY THE SAME; CONTINUOUSLY DISCHARGING SAID FURTHER GASEOUS PHASE, IN ADMIXTURE WITH THE FIRST-MENTIONED GASEOUS PHASE, FROM ABOVE SAID COLUMN OF LIQUID; AND CONTINUOUSLY WITHDRAWING LIQUID PHASE, SUBSTANTIALLY FREE FROM COMBUSTIBLES, FROM THE LOWER PART OF THE SECOND REACTION ZONE.

Nov. .19. 1914 MORGAN 3.849.536

war cowsusnon OF WASTE LIQUORS Filed Aug. 15', 1971 v 3 Sheets-Sheet '1DEGQEE 0F oxlbATiow ("1 oF THEOREUCAL o REACUON ME UN\TS Nov. 19, 1 974Filed Aug. 15, 1971 3 Sheets-Sheet 2 Nov. 19, 1974 J. E. MORGAN3,849,536

WET COMBUSTION OF WASTE LIQUORS Filed Aug. 13, 1971 I5 Sheets-Sheet 5United States Patent 3,849,536 WET COMBUSTION OF WASTE LIQUORS JohnEdward Morgan, Burnie, Tasmania, Australia, as-

signor to Associated Pulp and Paper Mills Limited, Melbourne, Victoria,Australia Filed Aug. 31, 1971, Ser. No. 176,651 Claims priority,application Australia, Aug. 31, 1970, 2,374/ 70 Int. Cl. C01d 1/04; C02b1/34; D21c 11/14 US. Cl. 423-206 2 Claims ABSTRACT OF THE DISCLOSUREMethod and apparatus for wet combustion of waste liquors such asobtained from the soda process for the pulping of wood comprisingsubjecting the waste liquor to a first stage oxidation treatment withair under pressure, separating inert gases and gaseous products ofoxidation from the partially oxidised liquid phase thereby reducing thepartial pressure of inert gases in equilibrium with the partiallyoxidised liquid phase, and subjecting the partially oxidised liquidphase to a second stage oxidation treatment with air under pressure.

This invention relates to improvements in the wet combustion of wasteliquors containing combustible organic materials and refers especiallyto improvements which facilitate the wet combustion of waste liquorobtained from the soda process for the pulping of wood, but theinvention has several concomitant advantages in relation to the wetcombustion of other waste liquors containing organic materials.

In the known art of wet combustion the waste liquor which containscombustible organic material in aqueous solution or in fine dispersionand also may contain in addition inorganic substances in solution ismixed with an oxygenating gas such as air under superatmosphericpressure and the temperature of the mixture is adjusted to or maintainedat a value not exceeding the critical temperature of water.

The aim of wet combustion is to bring about partially complete orsubstantially complete oxidation of the organic content of waste liquorsin the aqueous phase and whereby such organic content is partially orcompletely converted to the ultimate oxidation products of carbondioxide and water and thereby the organic content of the wasteeliminated or reduced to a desired degree. Where the organicconstituents contain in addition other elements such as sulphur,nitrogen or phosphorus it is noted that these will usually be oxidisedpartially or completely to their highest stable states of oxidationunder the prevailing conditions but applicants invention is independentof the presence or absence of such other constituents.

.It is an object of applicants invention to provide a new and improvedmethod and arrangement of apparatus for the carrying out of the processof wet combustion so as to secure a complete or substantially completeelimination of the organic content of a waste liquor, and a furtherobject is to enable the wet combustion process to be used for thisobjective in a more practicable and economical manner than previouslyavailable.

Applicants invention provides a method of securing a complete orsubstantially complete elimination of the organic content of the wasteliquor from the soda process of wood pulping, thereby facilitating thesubsequent recovery of the inorganic chemical materials of value in suchwaste liquor after the wet combustion process, and applicants method isalso applicable to other types of waste liquors when it is desired forany reason to secure the substantially complete removal of its organiccontent.

3,849,536 Patented Nov. 19, 1974 When the wet combustion method can bearranged to achieve substantially complete oxidation of the carboncontent of the organic material to carbon dioxide and the hydrogencontent of the organic material to water the net and final result issubstantially equivalent to that achieved by normal dry combustion ofthe same organic material in the presence of an excess of oxygen overthe theoretical requirement and, as regards the net overall chemicalreaction and the exothermic heat of reaction associated with suchreaction, is substantially identical in both cases.

Dry combustion of an organic material in the presence of a reasonableexcess of oxygen above theoretical true requirement normally proceeds tocompletion very rapidly when the temperature is high and flame ispresent. The ignition point of dry organic materials varies widelydepending on their composition but, for example, in the case of purecarbon is of the order of l,200 F. and after ignition the flametemperatures are much higher to the order of 3,000 F. or higher. Undersuch conditions the combustion or oxidation reactions are very rapid andcomplete and intermediate stages are not readily defined or identified.

Wet combustion, by definition, must proceed in the aqueous phase and attemperatures not exceeding the critical temperature of water (705.4 F.)and in practice it is limited to temperatures of the order of 600 F. dueto excessive evaporation of water as the critical tempera ture of Wateris more closely approached.

In wet combustion the necessity to use such low temperatures relative tothose which apply in dry combustion, combined with the situation thatthe organic concentration in aqueous waste liquors is usually low, ofthe order of ten per centum by weight, results in relatively slow ratesfor the oxidation or combustion reactions such that these may be onlypartly complete unless impracticably long terms of reaction areemployed.

In the case of wet combustion of soda process waste liquor applicant hasfound that the organic content can be eliminated to the extent of aboutninety per centum of that originally present in relatively shortreaction times but complete oxidation of the balance of the organicmaterial to carbon dioxide and water requires a total reaction time inexcess of that economically practicable. Similar observations in respectof other waste liquors have been noted by applicant.

For soda process Waste liquor, applicant discloses a typical relationbetween the percentage of organic material completely oxidised and thetime of reaction for such degree of oxidation expressed in arbitraryunits, and this is shown in FIG. 1 of the accompanying drawings fromwhich it is observed that theoretically complete oxidation is approachedonly asymptotically with time.

In the case of soda process waste liquors and in a wide range of wasteliquors containing organic materials a great variety of complexity ofthe organic compounds present has been observed, and it has also beenfound that whereas some of these compounds are readily oxidised othersare more resistant to oxidation in varying degrees.

Applicants studies and experiments have shown that in the process of wetcombustion some organic materials may be oxidised rapidly andsubstantially by a more or less direct route to carbon dioxide and waterwhile in other cases they may be converted into other clearly definedorganic compounds representing intermediate stages of oxidation, whichcompounds are relatively resistant to complete oxidation except undermore severe conditions or long reaction times.

For example, in the case of soda process waste liquor and other similarwaste liquors from wood pulping operations applicant has observed that asubstantial proportion of the lignin and other humic materials of highmolecular weight derived from wood and present in the liquor oxidisesubstantially and directly to carbon dioxide and water but in additionproduce as intermediate products a smaller proportion of low molecularweight carboxylic acids normally in the form of sodium salts, such assodium acetate and related acids or acid salts, which are found torequire longer reaction times and generally more severe conditions fortheir ultimate complete oxidation.

In the treatment of soda process waste liquor by the wet combustionprocess one objective is to eliminate to the maximum possible extent allorganic materials and in particular those which are combined chemicallywith sodium since it is usually desired to recover the sodium valuesfrom the treated liquor. Sodium-organic compounds such as sodium acetatecannot be readily converted to forms such as sodium carbonate, sodiumbicarbonate or sodium hydroxide which are desired for recovery of sodiumvalues.

The above description of the advantages and objectives of the applicantsinvention in relation to soda process waste liquor does not exclude itsadvantageous application to other types of waste liquors where similarproblems may exist and where very high degrees of elimination ofresidual organic material are desired for similar or other reasons.

Applicant has found with reference to FIG. 1 that the bulk of theoxidation of the high molecular weight compounds which represent up toninety per centum of the total organic material in soda process wasteliquor is controlled by mass transfer and that large interfacial contactareas are advantageous.

Applicant has further found that where such primary oxidation of thebulk of the organic material gives rise in part to a compound such assodium acetate, in the case of soda process waste liquor, the furtheroxidative reactions needed to convert such sodium acetate or related orsimilar substances to carbon dioxide and water are controlled by otherfactors such as the partial pressure of oxygen and the residualconcentration of the organic materials in the aqueous phase, and it hasalso been found that such residual concentration continually diminishesas the reaction proceeds to theoretical completion. For example,applicant has found that in the case of the sodium acetate residualarising after the partial wet combustion of soda process black liquor,this sodium acetate further oxidises to carbon dioxide and water at areaction rate described by the following equation (1).

[C =concentration of sodium acetate.

[C =concentration of oxygen.

x=order of reaction with respect to sodium acetate. y=order of reactionwith respect to oxygen. k=reaction rate constant dC /dt=rate ofdecomposition of sodium acetate.

From the above equation, applicant has deduced that whereas theconcentration of sodium acetate (C cannot be varied easily and willdiminish continuously as the reaction proceeds, the reaction rate, thatis the rate of decomposition to carbon dioxide and water, can besubstantially increased by increasing the partial pressure of oxygen incontact with the liquid phase.

In the known art of wet combustion the oxygen in the form of air orother oxygenating gas is mixed under suitable pressure and temperatureconditions with the waste liquor and is usually arranged to flowco-currently with the liquor through the reaction space the volume ofwhich is adjusted to allow sufiicient reaction time for the reaction toproceed to the desired degree of completion. Alternatively, after mixingthe reaction may be allowed to proceed for any given time in a batchtype of reactor.

In the above embodiments of the prior art it is obvious that after thebulk of the reaction is completed the con centration of residual organicmaterial is low and additionally the oxygen partial pressure is lowbecause it is neither practical or economic to employ a large excess (foxygen above that theoretically required, and in practice such excess isusually adjusted to the order of 0.5 to 1.0 per centum above thetheoretical amount which can be calculated or otherwise determined.

According to applicants invention the introduction of oxygen, usually inthe form of air or other oxygen-containing or oxygenating gas (referredto in this specification and in the claims as air) is etfected in notless than two stages, each stage being conducted either co-currentlywith the liquor or countercurrently with the liquor, and the proportionof air added at each stage is related to the amount of oxidationrequired in each stage. Further, between each stage of oxidation thegaseous products of oxidation, namely carbon dioxide and some watervapour, are separated from the partially oxidised liquid phase togetherwith the inert nitrogen content of the air employed (or other inertconstituents of the oxygenating gas) thus reducing the partial pressureof inert gases and carbon dioxide (hereinafter referred to as inertgases) in equilibrium with the liquid phase. The balance of aircontaining the requisite oxygen is then introduced into the partiallyoxidised and separated liquid or aqueous phase whereby the partialpressure of oxygen will be higher than would be obtainable in the caseof the prior art where it would be relatively low due to the carbondioxide from the prior oxidation reactions and also the presence of theresidual nitrogen or other inert components of the air.

The temperature of the liquid phase in the first stage and in the secondstage of the process is preferably maintained between 450 F. and 705.4F. In each case the temperature is preferably maintained between 600 F.and 625 F. The pressure is preferably maintained between 70 and 225atmospheres.

In one form of applicants invention pure oxygen or substantially pureoxygen or oxygen-rich gas rather than air or other dilute oxygenatinggas may be used in the second or later stages of the process to achievethe highest possible partial pressure of oxygen. Whereas substantiallypure oxygen could be theoretically used in the first stage of oxidationthis is restricted in practice because the reaction may proceed withexplosive violence in the presence of a relatively high concentration ofreadily oxidisable organic material existing at the beginning of theprocess.

As Well as the increase in the rate of oxidation made possible by theapplicants invention, there are several concomitant advantages. In theprior art the degree of oxidation of organic material could not beeasily controlled since the volume of the vessel in which reaction takesplace could not be easily changed, provided of course that sufficientoxygen was present for substantially complete oxidation.

Applicant's invention allows the volume available for reaction to becontrolled easily by raising or lowering the level of the liquid phasein the second or later stages of oxidation.

A further advantage in the case of soda process waste liquor or othercarbonate-containing liquors is the substantial reduction in the sodiumbicarbonate content of the oxidised liquor which is brought about by thecountercurrent flow of the air or oxygenating gas used in the second orlater stages or oxidation, such air being substantially free of carbondioxide and thereby reducing the partial pressure of carbon dioxide inand above the liquid phase. The reduction in sodium bicarbonate contentreduces the quantity of calcium hydroxide required for the conversion ofthe soda-containing oxidised liquor to sodium hydroxide, such conversionand recovery of sodium in the form of sodium hydroxide values being theusual final objective of the process.

The above concomitant advantages are not restricted to soda processwaste liquors but may apply to a wide range of situations such as othercarbonate-containing waste liquors which may contain metals other thansodium as major inorganic constituents.

For a practical embodiment of the invention in a wet combustion systemreference is made to FIGS. 2A to 5 of the accompanying drawings toillustrate a suitable apparatus, but this in no way restricts theprinciple of applicants invention to this particular form of apparatus.In these drawings:

FIGS. 2A and 2B are views in sectional elevation of a pressure vesselfitted with apparatus for carrying out the invention, FIG. 2A showingthe lower part of the vessel and FIG. 2B the upper part.

FIG. 3 is a view in sectional plan taken on the line 3-3 of FIG. 2A,

FIG. 4 is a -view in sectional plan taken on the line 44 of FIG. 2B, and

FIG. 5 is a view in sectional plan taken on the line 5-5 of FIG. 2B.

The apparatus shown in the drawings provides for a two-stageintroduction of air with one stage of separation embodied between thefirst and second stages of oxidation and further embodies a co-currentflow of air and waste liquor in the first stage with a countercurrentflow of air and partially oxidised liquor in the second stage thusachieving maximum efliciency of oxidation in this stage.

Further, in this particular embodiment of the invention the separatorvolume provided for the separation of gas and liquid between the firstand second stage is also used simultaneously for separation after thesecond stage thus achieving a practical constructional advantage in theapparatus.

In the apparatus shown in the drawings, the reference numeral indicatesan elongated vertical pressure vessel or reactor, having a lower zone 11in which the first reaction stage of the Wet combustion process takesplace, and an upper zone 12 in which the second reaction stage takesplace. For convenience of illustration, the liquors present in thevessel 10 are not shown.

The lower zone 11 is separated from the upper zone 12 by an imperforateplate 13 which is secured at its outer edge to a ring 14 mounted on theinner wall of the vessel 10 and at its inner edge to a plate 15 securedto the lower end of a vertical pipe 16 arranged centrally in the vessel10. The pipe 16 is formed in sections which are secured together atjunctions 17. The lower end of the pipe 16 communicates with the lowerzone 11 and its upper end communicates with a separating anddistributing device 18 which is described below.

A series of perforated baffles 20 are arranged at vertically spacedintervals in the upper zone 12, each perforated baffle (which is shownmore fully in FIG. 4) having a large number of perforations 21 and beingsupported between a ring 22 on the inner Wall of the vessel 10 and aring-shaped support 23 secured to the pipe 16.

The separating and distributing device 18 comprises two curved pipes 25and 26 which are connected at their inner ends to the upper end of thepipe 16 and are attached at their outer ends to the inner wall of thevessel 10 by brackets 27. The pipes 25, 26 are shaped so as to delivermaterial from their outer ends in a tangential direction adjacent to theinner wall of the vessel 10 (see FIG. 5).

Referring to FIGS. 2A and 3, an inlet nozzle 30 is provided at the lowerend of the vessel 10 within the zone 11, entering the vessel at flange31. A secondary air inlet pipe 32 is provided to extend through the wallof the vessel 10 at a short distance above the plate 13, that is, at thelower part of the upper zone 12, and the inlet pipe 32 is connected toan air disperser 33 within the vessel 10 which consists of two circularpipes 34 and a series of radial pipes 35 all of which are provided withperforations 36 in their surfaces (see FIG. 3).

A liquor discharge outlet pipe 38 is provided to extend through the wallof the vessel 10 at the lower end of the upper zone 12.

A gas discharge vent 39 is provided at the upper end of the vessel 10. Atemperature nozzle 40 and a sampling nozzle 41 are provided at suitablepositions in the wall of the vessel 10.

The level of the liquid in the zone 12, which may be varied up or downas described below, is indicated diagrammatically at 42.

Air and black liquor are admitted to the zone 11 through nozzle 30, andair is admitted through inlet 32 and disperser 33 to the bottom of thesecond reaction zone 12. The central pipe 16 communicates between thefirst reaction stage 11 and the separating and distributing device 18,at the upper end of the reactor. Liquor is dis charged from the outlet38 located near the lower end of the second reaction zone 12.

The apparatus of FIGS. 2A to 5 was used to process waste liquor,hereinafter called black liquor, derived from the soda process ofpulping wood. The black liquor was processed on a continuous basis usingthe wet combustion process.

A mixture of air and black liquor comprising about 221.5 lb./min.nitrogen, about 66.5 lb./min. oxygen, about 555 lb./min. water and about73 1b./min. total dissolved solids (such 73 lb./min. of solids includingabout 23 lb./min. of sodium in combined form but calculated andexpressed as the equivalent weight of sodium hydroxide) at asuperatmospheric pressure of about 210 atmospheres and preheated toabout 300 F. was introduced continuously to the first reaction stage 11of the reactor 10 via the inlet nozzle 30 and a suitable disperser (notshown) consisting of a single or multiple orifice arrangement designedto produce high turbulence and large interfacial areas for gas andliquid phase contact. The proportion of oxygen introduced in this firststage of oxidation was about of that theoretically required forsubstantially complete oxidation.

The mixed gases and liquor were passed upwardly and co-currently throughthe first reaction stage 11 wherein oxidation of the organic materialproceeded exothermally with the process controlled so that thetemperature was about 608 F. and the total system pressure wasmaintained at about 210' atmospheres.

Partial oxidation of the organic materials in the black liquor wasachieved during passage of the mixture through the first reaction stage11 and about 29 lb./min. of water and about 86 lb./hr. of-carbon dioxidewere formed as reaction products, but about 19' lb./hr. of this carbondioxide produced was found to be chemically combined with sodium in theform of sodium carbonate and/or sodium bicarbonate or was partly as asolution of gas in the aqueous phase. The partially oxidised liquorwhich resulted from this final oxidation stage comprised about 7.5lb./min. of unoxidised organic material mainly in the form of sodiumacetate together with the sodium in combined form present in theoriginal black liquor.

After the first reaction stage 11 the mixture of partially oxidisedliquor and gases was caused to pass upwards through the central tube 16to the separating device 18 which discharged into the upper portion ofthe reactor where the gas phase and liquid phase were separated. The gasmoved upwards and was vented from the reactor via the discharge vent 39.The partially oxidised liquor was arranged to move downwards and enteredthe second reaction zone 12.

A large proportion of the exothermic heat generated in the firs-treaction zone 11 was transferred by conduction and convection to thesecond reaction zone 12 in such amount that the temperature of thesecond reaction zone 12 was maintained at about 608 F.

Air comprising about 24.5 lb./min. nitrogen and about 7.5 lb./min.oxygen was introduced continuously to the lower section of the secondreaction zone 12 via the inlet pipe 32 and the disperser 33. This airmoved upwards against the downwardly flowing liquor and through theperforated bafiies 20 designed to cause intimate mixing of the gas andliquid at that point and to provide hydrodynamic conditions in thesecond reaction zone 12 conducive to maximum decomposition of theremaining organic material.

When the downwardly flowing liquor reached the outlet nozzle 38substantially complete oxidation was found to be achieved provided thelevel 42 of the liquid in this second reaction zone 12 had beenmaintained at a suitable level related to the desired retention time inthis zone. By controlling the rate of discharge of the liquor from theoutlet 38, the level 42 of the liquor in the zone 12 could be lowered,or raised, thereby varying the volume of liquid in contact with theoxygenating gas and providing a control of the amount of organicmaterial completely or substantially completely oxidised.

It was found that in the apparatus of FIGS. 2A to 5 I the partialpressure of oxygen immediately after entry to the second reaction zone12 was approximately 23 atmospheres which is the same as the partialpressure of oxygen immediately after entry to the first reaction zone11. In the prior art the partial pressure of oxygen assuming 90% of theorganic material had been decomposed would have been approximately twoatmospheres. Applicant has found that the values of 3 :05 and x=1.0apply to equation (1) for the specific case of oxidation of sodiumacetate. It is then evident that at least a ten-fold increase in oxygenpartial pressure is available during the final 10% of the oxidationreaction which equation (1) shows to result in an increase in the rateof decomposition of about three to four times, thus achieving the objectof applicants invention.

What is claimed is:

1. A two-stage continuous method of wet combustion of a waste liquorobtained from the soda process for the pulping of wood and containingcombustible components, which method comprises the serially succeedingsteps of mixing a stream of the waste liquor with heated oxygenating gasunder pressure;

passing the mixture at a temperature between 450 and 705.4 F. and undera pressure between 70 and 225 atmospheres upwardly through a firstreaction zone in the lower compartment of a generally vertical pressurevessel wherein to effect combustion of a major part of the combustiblescontent of the stream into an inert gaseous phase comprising carbondioxide and steam, with generation of heat;

passing the resulting partially oxidized mixture composed of gaseousphase and liquid phase, at elevated temperature, under pressure upwardlyinto a second reaction zone in an upper compartment of said pressurevessel, the said partially oxidized mixture being passed as a streamupwardly through but out of direct contact with liquid phase in thesecond reaction zone and being then distributed into said secondreaction zone above such liquid phase; separating the said inert gaseousphase from liquid phase of the partially oxidized mixture in the upperpart of the second reaction zone, discharging the said inert gaseousphase from the upper part of the said second reaction zone, therebyreducing the partial pressure of the inert gaseous phase in equilibriumwith the said liquid phase, causing the separated liquid phase to flowdownwardly as a column of liquid in said second reaction zone, thetemperature of the downwardly flowing column of liquid being at atemperature between 450 and 705.4 F. and under a pressure between and225 atmospheres; subjecting the residual combustibles content to saiddownwardly flowing column of liquid, substantially free from theaforesaid gaseous phase, to further oxidation treatment by passing anoxygenating gas under pressure upwardly through said column of liquid,thereby forming a further gaseous phase and a substantiallycombustibles-free liquid phase, the partial pressure of oxygen incontact with the liquid phase in the second reaction zone being at leastas great as the partial pressure of oxygen in contact with the liquidphase in the first reaction zone, and the temperatures in the firstreaction zone and in the second reaction zone being substantially thesame; continuously discharging said further gaseous phase, in admixturewith the first-mentioned gaseous phase, from above said column ofliquid; and continuously withdrawing liquid phase, substantially freefrom combustibles, from the lower part of the second reaction zone. 2. Amethod according to claim 1 wherein oxygen or oxygen-rich gas is used inthe second stage treatment.

References Cited UNITED STATES PATENTS 1,404,708 1/19-22 Allbright260-409 3,574,051 4/1971 Shah 23--48 X 3,617,033 11/1971 Ichikawa et al.23285 MILTON WEISSMAN, Primary Examiner U.S. Cl. X.R.

1. A TWO-STAGE CONTINUOUS METHOD OF WET COMBUSTION OF A WASTE LIQUOROBTAINED FROM THE SODA PROCESS FOR THE PULPING OF WOOD AND CONTAININGCOMBUSTIBLE COMPONENTS, WHICH METHOD COMPRISES THE SERIALLY SUCCEEDINGSTEPS OF MIXING A STREAM OF THE WASTE LIQUOR WITH HEATED OXYGENATING GASUNDER PRESSURE; PASSING THE MIXTURE OF A TEMPERATURE BETWEEN 450* AND705*F. AND UNDER A PRESSURE BETWEEN 70 TO 225 ATMOSPHERES UPWARDLYTHROUGH A FIRST REACTION ZONE IN THE LOWER COMPARTMENT OF A GENERALLYVERTICAL PRESSURE VESSEL WHEREIN TO EFFECT COMBUSTION OF A MAJOR PART OFTHE COMBUSTIBLES CONTENT OF THE STREAM INTO AN INERT GASEOUS PHASECOMPRISING CARBON DIOXIDE AND STEAM, WITH GENERATION OF HEAT; PASSINGTHE RESULTING PARTIALLY OXIDIZED MIXTURE COMPOSED OF GASEOUS PHASE ATELEVATED TEMPERATURE, UNDER PRESSURE UPWARDLY INTO A SECOND REACTIONZONE IN AN UPPER COMPARTMENT OF SAID PRESSURE VESSEL, THE SAID PARTIALLYOXIDIZED MIXTURE BEING PASSED AS A STREAM UPWARDLY THROUGH BUT OUT OFDIRECT CONTACT WITH LIQUID PHASE IN THE SECOND REACTION ZONE AND BEINGTHEN DISTRIBUTED INTO SAID SECOND REACTION ZONE ABOVE SUCH LIQUID PHASE;SEPARATING THE SAID INERT GASEOUS PHASE FROM LIQUID PHASE OF THEPARTIALLY OXIDIZED MIXTURE IN THE UPPER PART OF THE SECOND REACTIONZONE, DISCHARGING THE SAID INERT GASEOUS PHASE FROM THE UPPER PART OFTHE SAID SECOND REACTION ZONE, THEREBY REDUCING THE PARTIAL PRESSURE OFTHE INERT GASEOUS PHASE IN EQUILIBRIUM WITH THE SAID LIQUID PHASE,CAUSING THE SEPARATED LIQUID PHASE TO FLOW DOWNWARDLY AS A COLUMN OFLIQUID IN SAID SECOND REACTION ZONE, THE TEMPERATURE OF THE DOWNWARDLYFLOWING COLUMN OF LIQUID BEING AT A TEMPERATURE BETWEEN 450* AND705.4*F. AND UNDER A PRESSURE BETWEEN 70 AND D225 ATMOSPHERES;SUBJECTING THE RESIDUAL COMBUSTIBLES CONTENT OF SAID DOWNWARDLY FLOWINGCOLUMN OF LIQUID, SUBSTANTIALLY FREE FROM THE AFORESAID GASEOUS PHASE TOFURTHER OXIDATION TREATMENT BY PASING AN OXYGENATING GAS UNDER PRESSUREUPWARDLY THROUGH SAID COLUMN OF LIQUID, THEREBY FORMING A FURTHERGASEOUS PHASE AND A SUBSTANTIALLY COMBUSTIBLES-FREE LIQUID PHASE, THEPARTIALLY PRESSURE OF OXYGEN IN CONTACT WITH THE LIQUID PHASE IN THESECOND REACTION ZONE BEING AT LEAST AS GREAT AS THE PARTIAL PRESSURE OFOXYGEN IN CONTACT WITH THE LIQUID PHASE IN THE FIRST REACTION ZONE, ANDTHE TEMPERATURES IN THE FIRST REACTION ZONE AND IN THE SECOND REACTIONZONE BEING SUBSTANTIALLY THE SAME; CONTINUOUSLY DISCHARGING SAID FURTHERGASEOUS PHASE, IN ADMIXTURE WITH THE FIRST-MENTIONED GASEOUS PHASE, FROMABOVE SAID COLUMN OF LIQUID; AND CONTINUOUSLY WITHDRAWING LIQUID PHASE,SUBSTANTIALLY FREE FROM COMBUSTIBLES, FROM THE LOWER PART OF THE SECONDREACTION ZONE.